The invention relates to artifically inducing a blood pulse with a cuff for conducting blood tests with a pulse oximeter.
The existence of a blood pulse is necessary in a test for determining oxygen saturation of blood by a pulse oximeter. A typical pulse oximeter transmits light through a given area on a finger, a lobe of the ear or other blood containing body member. Infra-red and visible red light are commonly transmitted because it is known that the degree of absorption of red light is different for oxygenated vs. de-oxygenated blood and that the absorption of infra-red light is relatively insensitive to the level of oxygenation. The transmission of red and infrared light is detected by a photodiode which converts the different wavelengths of light to an electrical signal having an amplitude that is proportional to the intensities of the light transmitted. Thus, for every heartbeat, an analog signal known as a pulsatile waveform, which has maximum and minimum levels, is generated.
Using the signal generated by the infra-red light as a reference signal and the fact that tissue absorption is directly proportional to the log of the ratio of light transmitted to incident light, the percentage of oxygen saturation can be determined. The common approach for this determination is to link these signals to a computer for determining a ratio between the amplitude of the pulses for each wavelength during a heartbeat cycle. Since each ratio corresponds to a different percentage of oxygen saturation, the computer can be programmed to display from memory the percentage of oxygen saturation that corresponds to each ratio.